Method and apparatus for EMI shielding

ABSTRACT

Disclosed are methods for manufacturing electromagnetic interference shields for use in nonconductive housings of electronic equipment. In one embodiment, the shield may include an electrically nonconductive substrate, such as a thermoformable film, coated with an electrically conductive element, such as an extensible ink or a combination of conductive fibers with an extensible film. In one embodiment, a compressible conductive perimeter gap gasket may be formed by using a form in place process.

RELATED APPLICATIONS

[0001] This application incorporates by reference in its entirety andclaims priority to U.S. Provisional Patent Application Ser. No.60/185,597 entitled Methods and Apparatus for EMI Shielding filed onFeb. 28, 2000. This application also incorporates by reference in itsentirety and claims priority to U.S. patent application entitled Methodsand Apparatus for EMI Shielding filed on Jan. 24, 2001, Attorney DocketNo. APM-036.

FIELD OF THE INVENTION

[0002] This invention relates to methods of manufacturingelectromagnetic interference (“EMI”) shields and the EMI shieldsproduced thereby.

BACKGROUND OF THE INVENTION

[0003] As used herein, the term EMI should be considered to refergenerally to both EMI and radio frequency interference (“RFI”)emissions, and the term electromagnetic should be considered to refergenerally to electromagnetic and radio frequency.

[0004] During normal operation, electronic equipment generatesundesirable electromagnetic energy that can interfere with the operationof proximately located electronic equipment due to EMI transmission byradiation and conduction. The electromagnetic energy can be of a widerange of wavelengths and frequencies. To minimize the problemsassociated with EMI, sources of undesirable electromagnetic energy maybe shielded and electrically grounded. Shielding is designed to preventboth ingress and egress of electromagnetic energy relative to a housingor other enclosure in which the electronic equipment is disposed. Sincesuch enclosures often include gaps or seams between adjacent accesspanels and around doors, effective shielding is difficult to attain,because the gaps in the enclosure permit transference of EMItherethrough. Further, in the case of electrically conductive metalenclosures, these gaps can inhibit the beneficial Faraday Cage Effect byforming discontinuities in the conductivity of the enclosure whichcompromise the efficiency of the ground conduction path through theenclosure. Moreover, by presenting an electrical conductivity level atthe gaps that is significantly different from that of the enclosuregenerally, the gaps can act as slot antennae, resulting in the enclosureitself becoming a secondary source of EMI.

[0005] Specialized EMI gaskets have been developed for use in gaps andaround doors to provide a degree of EMI shielding while permittingoperation of enclosure doors and access panels. To shield EMIeffectively, the gasket should be capable of absorbing or reflecting EMIas well as establishing a continuous electrically conductive path acrossthe gap in which the gasket is disposed. Conventional metallic gasketsmanufactured from copper doped with beryllium are widely employed forEMI shielding due to their high level of electrical conductivity. Due toinherent electrical resistance in the gasket, however, a portion of theelectromagnetic field being shielded induces a current in the gasket,requiring that the gasket form a part of an electrically conductive pathfor passing the induced current flow to ground. Failure to ground thegasket adequately could result in radiation of an electromagnetic fieldfrom a side of the gasket opposite the primary EMI field.

[0006] In addition to the desirable qualities of high conductivity andgrounding capability, EMI gaskets in door applications should beelastically compliant and resilient to compensate for variable gapwidths and door operation, yet tough to withstand repeated door closurewithout failing due to metal fatigue, compression set, or other failuremechanism. EMI gaskets should also be configured to ensure intimateelectrical contact with proximate structure while presenting minimalforce resistance per unit length to door closure, as the total length ofan EMI gasket to shield a large door can readily exceed several meters.It is also desirable that the gasket be resistant to galvanic corrosionwhich can occur when dissimilar metals are in contact with each otherfor extended periods of time. Very low resistance and, concomitantly,very high electrical conductivity are becoming required characteristicsof EMI gaskets due to increasing shielding requirements. Low cost, easeof manufacture, and ease of installation are also desirablecharacteristics for achieving broad use and commercial success.

[0007] Conventional metallic EMI gaskets, often referred to as copperberyllium finger strips, include a plurality of cantilevered or bridgedfingers forming linear slits therebetween. The fingers provide springand wiping actions when compressed. Other types of EMI gaskets includeclosed-cell foam sponges having metallic wire mesh knitted thereover ormetallized fabric bonded thereto. Metallic wire mesh may also be knittedover silicone tubing. Strips of rolled metallic wire mesh, without foamor tubing inserts, are also employed.

[0008] One problem with metallic finger strips is that to ensure asufficiently low door closure force, the copper finger strips are madefrom thin stock, for example on the order of about 0.05 mm (0.002inches) to about 0.15 mm (0.006 inches) in thickness. Accordingly,sizing of the finger strip uninstalled height and the width of the gapin which it is installed should be controlled to ensure adequateelectrical contact when installed and loaded, yet prevent plasticdeformation and resultant failure of the strip due to overcompression ofthe fingers. To enhance toughness, beryllium is added to the copper toform an alloy; however, the beryllium adds cost and is a concern sinceberyllium is considered to be carcinogenic. Due to their thinness, thefinger strips are fragile and can fracture if mishandled oroverstressed. Finger strips also have thin sharp edges, which are asafety hazard to installation and maintenance personnel. Finger stripsare also expensive to manufacture, in part due to the costs associatedwith procuring and developing tooling for outfitting presses and rollingmachines to form the complex contours required. Changes to the design ofa finger strip to address production or performance problems require thepurchase of new tooling and typically incur development costs associatedwith establishing a reliable, high yield manufacturing process.Notwithstanding the above limitations, metallic finger strips arecommercially accepted and widely used. Once manufacturing has beenestablished, large quantities of finger strips can be made at relativelylow cost.

[0009] Another problem with conventional finger strips is that they arenot as effective in EMI shielding as clock speed of an electronicproduct is increased. As clock speed is increased, the wavelength of theEMI waves produced decreases. Accordingly, the waves can penetratesmaller and smaller apertures in the enclosure and in the EMI shield. Atlower wavelengths, the slits formed in the finger shields can act asslot antennae, permitting the passage of EMI therethrough and theresultant shielding effectiveness of the shields decreases. Conventionalfinger strips with linear slits formed between the fingers areincreasingly less effective in these applications.

[0010] Metallized fabric covered foam gaskets avoid many of theinstallation, performance, and safety disadvantages of finger strips;however, they can be relatively costly to produce due to expensive rawmaterials. Nonetheless, EMI gaskets manufactured from metallized fabricshaving foam cores are increasing in popularity, especially for use inequipment where performance is a primary consideration.

[0011] As used herein, the term metallized fabrics include articleshaving one or more metal coatings disposed on woven, nonwoven, or openmesh carrier backings or substrates and equivalents thereof. See, forexample, U.S. Pat. No. 4,900,618 issued to O'Connor et al., U.S. Pat.No. 4,910,072 issued to Morgan et al.; U.S. Pat. No. 5,075,037 issued toMorgan et al., and U.S. Pat. No. 5,393,928 issued to Cribb et al., thedisclosures of which are herein incorporated by reference in theirentirety. Metallized fabrics are commercially available in a variety ofmetal and fabric carrier backing combinations. For example, pure copperon a nylon carrier, nickel-copper alloy on a nylon carrier, and purenickel on a polyester mesh carrier are available under the registeredtrademark Flectron® metallized materials from Advanced PerformanceMaterials located in St. Louis, Mo. An aluminum foil on a polyester meshcarrier is available from Neptco, located in Pawtucket, R.I.

[0012] The choice of metal is guided, in part, by installationconditions of the EMI shield. For example, a particular metal might bechosen due to the composition of abutting body metal in the enclosure toavoid galvanic corrosion of the EMI shield, which could increaseelectrical resistance and deteriorate electrical grounding performance.Metallized tapes are desirable both for ease of application as well asdurability.

[0013] Metallized fabrics, such as those described in the O'Connor etal. patent mentioned hereinabove, are generally made by electrolessplating processes, such as electroless deposition of copper or othersuitable metal on a catalyzed fiber or film substrate. Thereafter one ormore additional layers of metal, such as nickel, may be electrolessly orelectrolytically deposited on the copper. These additional layers areapplied to prevent the underlying copper layer from corroding, whichwould increase the resistance and thereby decrease the electricalconductivity and performance of any EMI gasket made therefrom. Theadditional nickel layer on the copper also provides a harder surfacethan the base copper.

SUMMARY OF THE INVENTION

[0014] Two developments have been progressing independently for severalyears in the area of EMI shields for nonconductive enclosures, such asmolded plastic housings for cellular telephones, computers, and thelike. The first development is a form in place (“FIP”) process. See, forexample, U.S. Pat. No. 5,822,729 entitled Process for Producing a CasingProviding a Screen Against Electromagnetic Radiation, the disclosure ofwhich is incorporated herein by reference in its entirety. A goal of theFIP process is to produce a conductive and compressible elastomeric EMIgasket that can be directly applied to the substrate to be shielded,thereby eliminating the step of attaching the EMI gasket to theworkpiece at the assembly plant. One problem with the FIP process isthat it is necessary to have relatively complex and expensive dispensingequipment at the casting or molding plant, or at the assembly plant. Asthe capacity utilization of this equipment may be quite low, due to theuse on a single component this is a risky and potentially uneconomicsituation.

[0015] The second development in the area of EMI shielding is theproduction of conductive coatings, especially an extensible conductivecoating, which is a coating with high conductivity that can be appliedto a film, or other flexible substrate, that is later formed to adesired shape without substantial degradation of conductivity. See, forexample, U.S. Pat. No. 5,286,415 entitled Water-Based Polymer Thick FilmConductive Ink and U.S. Pat. No. 5,389,403 entitled Water-based PolymerThick Conductive Ink, the disclosures of which are incorporated hereinby reference in their entirety. Acheson Colloids Company, located atPort Huron, Mich., has developed a product based on silver ink that whencoated on a thermoformable film, such as General Electric's Lexan®,retains high electrical conductivity even when drawn to relatively highelongations. The thermoformable film may be formed to relatively complexthree dimensional shapes known as “cans.” The thermoformable film withextensible coating can replace conventional metal cans, as well asconductive painting and plating processes, used in mobile phones andother nonconductive small enclosures. The thermoformable film andextensible coating can also be part of larger electronic packages.

[0016] It has been discovered that thermoformable films, extensibleconductive coatings and FIP gaskets can be combined to produce integralEMI shields which can be readily manufactured and shipped from acentralized location to smaller assembly plants for installation intoelectronic equipment.

[0017] The EMI shield is manufactured from a polymer thick filmextensible conductive coating, that retains high electrical conductivityat high elongations, which is applied to a thermoformable film incombination with a FIP gasket. The EMI shield and FIP gasket provide EMIshielding of the entire interior of a given structure.

[0018] For example, suitable thermoformable films include LEXAN® andVALOX®, manufactured by the General Electric Company, Pittsfield, Mass.An example of a polymer thick film extensible conductive coating isElectrodag® SP-405, manufactured by Acheson Colloids Company, PortHuron, Mich.

[0019] Accordingly, in accordance with one embodiment, the invention isdrawn to a method for forming an EMI shield. The method includes thesteps of (a) providing a thermoformable film having a first side and asecond side; (b) applying an extensible conductive coating to thethermoformable film; (c) cutting the thermoformable film; (d)thermoforming the thermoformable film into a three-dimensional shape;and (e) applying a compressible EMI gasket to the thermoformable film,wherein steps (b) through (e) may be performed in any order.

[0020] In another embodiment the invention is drawn to an EMI shield.The EMI shield includes a thermoformable film having a first side and asecond side, wherein the thermoformable film is thermoformed into athree-dimensional shape; an extensible conductive coating applied to thethermoformable film; and a compressible EMI gasket attached to thethermoformable film.

[0021] In yet another embodiment, the extensible conductive coatingincludes an extensible film and conductive fibers. In another embodimentthe glass transition temperature of the extensible film is lower thanthe glass transition temperature of the thermoformable film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and further advantages of this invention may be betterunderstood by referring to the following description, taken inconjunction with the accompanying drawings, in which:

[0023]FIG. 1 is a process diagram of an embodiment of the currentinvention of a variety of methods for combining a formable nonconductivesubstrate with a conductive coating and a FIP gap gasket;

[0024]FIG. 2 is a schematic diagram of a conductive coating on athermoformable film;

[0025] FIGS. 3A-3C are schematic diagrams of embodiments of a simple anda more complex thermoformed EMI shield;

[0026] FIGS. 4A-4C are process steps for contouring a thermoformablefilm;

[0027]FIG. 5 is a table summarizing surface conductivity and shieldingeffectiveness test results of conductive coatings made of variousconductive materials and thermoformable materials; and

[0028]FIG. 6 is a schematic diagram of a FIP process on a contouredsubstrate.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Examples of a process for manufacturing embodiments of EMIshields are illustrated in FIG. 1.

[0030] In a first step, the EMI shield is manufactured from athermoformable film, such as General Electric's Lexan®. Thethermoformable film may be in small or large sheets or a long continuousreel, depending on the scale of production required. Generally, aformable film may be used and, in addition, non-formable films may beused if the required shape is flat.

[0031] The thermoformable film is coated with a conductive extensibleink, such as Acheson Colloids Company's Electrodag® SP-405 ink to forman extensible conductive coating. The extensible ink may be anyextensible ink in the case of a 3-D shape, and any conductive ink (orpaint or plating) in the case of 2-D shapes. The extensible ink can beapplied to the film by a variety of printing or film coating processes,such as flexographic printing, screen printing, gravure printing, offsetprinting, letter press printing, pad printing, slot coating, floodcoating, spray coating, and jet printing.

[0032] Depending on the configuration of the part used during theforming process, there can be a considerable amount of elongation of theEMI shield where geometric features of the shield are concentrated. Thisin turn may put excessive stress on the extensible ink. If theelongation of the extensible ink is too severe, this will result infracture of the conductive layer, which in turn leads to loss ofconductivity and loss of shielding. Ideally, the conductive layer wouldbe one that could be stretched infinitely over the entire part. Inpractice, this is difficult as most highly conductive materials willtend to fracture. Also, materials that are best for stretching aregenerally not conductive enough to be used as conductive shields.

[0033] In another embodiment the extensible conductive coating can beformed from a combination of conductive fibers with an extensible film.The extensible film can be selected from materials that, in general,have a lower glass transition temperature than the thermoformable filmand, in one embodiment, can be a polymer. The polymer selected for usewith the conductive fibers can be very thermoplastic, to the point ofalmost becoming a liquid, which results in a combined polymer/conductivefiber layer that becomes highly compliant to changes in geometry causedby thermoforming the thermoformable film, while the conductive fiberscontinue to interact with negligible loss of conductivity. FIG. 2illustrates an extensible conductive coating 20 on a thermoformable film30.

[0034] In one embodiment the conductive fibers can be placed on thethermoformable film and the extensible film can be placed on top of theconductive fibers. The arrangement of the thermoformable film, theconductive fibers, and the extensible film can be laminated to allow theconductive fibers to integrate with the extensible film. In anotherembodiment, the extensible film can be processed into fibers which canbe mixed with the conductive fibers. The mixture of conductive fibersand the fibers from the extensible film can be deposited on thethermoformable film at a temperature which at least partially melts theextensible film fibers.

[0035] Materials for the conductive fibers include stainless steelfibers from Baeckert, Naslon—SUS316L from Nippon Seisen Co. ofOsaka-City, Japan, Panex Chopped Fiber—PX33CF1000-01 from ZoltexCorporation of St. Louis, Mo., and X-Static Silver Nylon Fiber fromInstrument Specialties of Scranton, Pa. Any fiber which is at leastabout 3.175 mm (0.125 inches) long and less than about 0.254 mm (0.01inches) in diameter may be used, provided that the outer surface of thefiber is coated with metal sufficient to produce bulk conductivity ofthe material to less than about 50 milliohm-cm, preferably less thanabout 25 milliohm-cm, more preferably less than bout 10 milliohm-cm, asdetermined by Mil-G-83528 paragraph 4.6.11/ASTM 991. Pure componentfibers can be used as well, provided the bulk resistivity is below aboutthese values. In addition, some other conductive materials that can beused are silver loaded particles, silver/copper flake, silver/nylonfiber, silver carbon fibers, tin over copper flash, and tin.

[0036] Materials for the extensible film include polypropylene andpolyethylene fibers or films, both available from Dow Chemicals. Othersuitable polymers for the extensible film include polystyrene,acrylonitrile-butydiene-styrene (ABS), styrene-acrylonitrile (SAN),polycarbonate, polyester, and polyamide, as long as the thermoplasticpolymer has a lower glass transition temperature than the supportingpolymer shield, for example at least about 20 degrees C lower.Additionally, a silicone material can also be used for the extensiblefilm.

[0037] The extensible conductive coating can be made by blendingpolyethylene and/or polypropylene fibers with the conductive fibers andcalendering or laminating the composite with the thermoformable film.Other methods for applying the extensible conductive coating to thethermoformable film include wet coating, carding, plating, coating,flocking, dry laid screening, and vacuum metal/ion sputter techniques.

[0038] Various combinations and permutations of the material for theconductive fibers, the material for the extensible film, and the methodof applying the extensible conductive coating made from the extensiblefilm and conductive fibers to the thermoformable film can be chosen toresult in a desired surface conductivity and shielding effectiveness ofthe EMI shield.

[0039] In some embodiments the conductive coating may be applied to bothsides of the thermoformable film. In other embodiments the conductivecoating may be applied to one side of the thermoformable film. Theconductive coating may be applied uniformly, or may be applied in apattern, such as a grid. In still other embodiments the conductivecoating may be applied in discrete areas or zones.

[0040] In a second step, the resulting coated film is then cut to thedesired 2-D shape. Any cutting process known to those skilled in the artcan be used such as water jet cutting, laser cutting die-cutting, hotwire cutting, etc. The film can be cut to produce a single shape or aplurality of similar or different shapes, which can be held together bysprues.

[0041] Next, in a third step, the cut film is thermoformed into thedesired 3-D shape. Any method of thermoforming known to those skilled inthe art may be used. The complexity of the 3-D shape can varysignificantly, from a simple box, formed by a single rectangle draw, toa multi-chamber part with different chamber sizes and depths. See FIGS.3A-3C for examples.

[0042] One method of thermoforming, positive forming, is illustrated inFIGS. 4A-4C. The thermoformable film 30 and the extensible conductivecoating 20 are heated by a heater 50 to soften the thermoformable film30 and the extensible conductive coating 20. The thermoformable film 30and extensible conductive coating 20 are then applied to a mold 60 and avacuum 70 drawn to conform the thermoformable film 30 and the conductivecoating 20 to the mold 60. Once cooled sufficiently, the contouredthermoformable film 30 and extensible conductive coating 20 are removedfrom the mold 60.

[0043] Lastly, a conductive elastomer gasket is dispensed onto thecoated thermoformed film in any desired pattern, using FIP dispensingequipment described below and illustrated in FIG. 6. The FIP gasket istypically applied about a perimeter, edge, lip, or other similarstructure; however, in more complex parts, the FIP gasket may be appiedto internal or external walls, dividers, or other similar surfacesforming with adjoining structure in the final assembled component orhousing. The conductive elastomer gasket is then cured, either atambient temperature or via elevated temperatures, for example, in acontinuous oven.

[0044] In addition to using FIP methods for manufacturing the elastomergasket, other gaskets known to those skilled in the art for shieldingEMI can be used. For example, the gasket may be other than conductiveelastomers including, but not limited to, metallized fabric wrapped foamgaskets, metal fingers, knitted gaskets, a printable foamable ink, etc.In some cases, the finished component may incorporate a separateenvironmental gasket, for example a polyurethane gasket.

[0045] The finished shielding element is then shipped to the assemblyplant, where the entire shielding function is accomplished by simplyplacing this single piece into an enclosure. Examples of shieldingcomposite cross-sections are shown in FIG. 1, FIG. 3C, and FIG. 4.

[0046] Note that the four general process steps do not have to beperformed in this particular order and, in fact, may be performed in anyorder. For example, the FIP gasket may be applied either before or aftercoating, cutting, or forming. Similarly, the coating may be appliedeither before or after cutting, forming, or application of the FIPgasket.

[0047]FIG. 5 is a table which shows a summary of surface conductivityand shield effectiveness test results for various conductive coatings.The table shows the conductive materials, the base extensible films, andthe manufacturing methods for applying the conductive coating to thethermoformable film. The table also shows the thickness of theconductive coating and exemplary draw amounts of the conductive coating.The test results of surface conductivity and shielding effectiveness areprovided for both an unformed conductive layer, after application of theextensible conductive coating to the thermoformable film and for aformed conductive layer after three-dimensional forming of the EMIgasket. The test results generally show the surface conductivityincreases after the conductive layer has been three-dimensionallyformed. The test results also generally show, with the exception of Agparticle ink, that the shielding effectiveness (SE) remains relativelyconstant before and after being three-dimensionally formed.

[0048] There are a number of ways to make a form in place gasket. Forexample, as illustrated in FIG. 6, is an embodiment of a method 100 formanufacturing an EMI shield made of conductive particles and a foamablemixture. In one embodiment, conductive particles 105, for example,chopped metal fibers or metallized polymer fibers, are added to thecomponents of a foamable mixture. The components of the foamable mixturecan be a polyol component 110 and an isocyonate component 115 of aurethane mixture. The polyol component 110, the isocyonate component115, and the conductive particles 105 are mixed in one or more mixingheads 125 to produce a urethane mixture with an integral network ofconductive particles 120.

[0049] The urethane mixture with the integral network of conductiveparticles 120 is then processed by available means to produce thedesired size and shape of a conductive EMI gasket. In one embodiment,the urethane mixture with an integral network of conductive particles120, is dispensed through a nozzle 130 directly onto a surface 135 of anelectrical enclosure 140 using an xyz positioning system 145 to form theEMI gasket in place as the mixture 120 foams and cures.

[0050] FIP EMI gaskets may be manufactured of conductive foams, wherethe conductive elements are introduced into the foam matrix prior tocasting by adding organo-metallic compounds to the foam chemical matrix,which are reduced to conductive elements during the foaming process.

[0051] Additionally, various forms of carbon may be added to urethanefoam chemical precursors to produce foams with surface resistivities of100 to 1000 ohms/square. These materials, however, have limited use inEMI shielding applications, due to the relatively high resistivity. Anew process produces conductive foams which are less than 10 ohms/squareby introducing more highly conductive materials into the foam chemicalprecursors, including silver-plated glass spheres, sintered metalparticles which have bulk resistivities below about 10⁻⁵ ohm-cm (e.g.Cu, Al, Ni, Ag), and silver-plated copper particles. Other conductivematerials include the class of non-metallic materials referred to asconductive polymers. This would include such materials as poly-Analine.

[0052] Another method of producing conductive foam is to produce theconductive elements in the foaming process by reacting organo-metalliccompounds during the foaming process. This is accomplished byintroducing reducing agents into one of the two or more chemicalprecursors of the foam prior to foaming. One example of these compoundsis copper acetate, but any metal compound, which is compatible with oneof the chemical foam precursors, could be used.

[0053] Examples of chemical foam systems which may be used include thevery broad range of urethane foams including polyester and polyethertypes. Chloroprenes, more commonly known as neoprene rubber foams, couldalso be used.

[0054] Variations, modifications, and other implementations of what isdescribed herein will occur to those of ordinary skill in the artwithout departing from the spirit and the scope of the invention.

What is claimed is:
 1. A method of forming an EMI shield comprising thesteps of: (a) providing a thermoformable film comprising a first sideand a second side; (b) applying an extensible conductive coating to thethermoformable film; (c) cutting the thermoformable film; (d)thermoforming the thermoformable film into a three-dimensional shape;and (e) applying a compressible EMI gasket to the thermoformable film,wherein steps (b) through (e) may be performed in any order.
 2. Themethod of claim 1 wherein the thermoformable film of step (a) is drawnfrom a roll.
 3. The method of claim 1 wherein the step (b) of applyingan extensible conductive coating to the thermoformable film is selectedfrom the group consisting of printing processes and film coatingprocesses.
 4. The method of claim 3 wherein the group of printingprocesses and film coating processes comprise flexographic printing,screen printing, gravure printing, offset printing, letter pressprinting, pad printing, slot coating, flood coating, spray coating, andjet printing.
 5. The method of claim 1 wherein the step (b) of applyingan extensible conductive coating to the thermoformable film comprisesapplying the extensible conductive coating to at least one of the firstside and the second side of the thermoformable film.
 6. The method ofclaim 5 wherein the extensible conductive coating is appliedsubstantially uniformly to the at least one of the first side and thesecond side of the thermoformable film.
 7. The method of claim 5 whereinthe extensible conductive coating is applied selectively to at least onezone and not to another zone on the at least one of the first side andthe second side of the thermoformable film.
 8. The method of claim 1wherein the EMI gasket of step (d) is selected from the group consistingof conductive elastomer, fabric wrapped foam, metal fingers,polyurethane, and knitted gaskets.
 9. The method of claim 1 wherein thestep (d) of applying the EMI gasket to the thermoformable film comprisesthe steps of: mixing conductive particles with foamable materials toform a foam mixture with an integral network of conductive particles;and processing the foam mixture with the integral network of conductiveparticles to shape the EMI gasket.
 10. The method of claim 9 wherein thefoamable materials are a polyol component and an isocyonate componentwhich form a urethane foam mixture.
 11. The method of claim 10 whereinthe step of processing the urethane foam mixture with the integralnetwork of conductive particles to shape the EMI gasket comprises movingthe surface of the thermoformable film relative to a nozzle supplyingthe urethane foam with the integral network of conductive particles toform the EMI gasket in place.
 12. The method of claim 9 wherein theconductive particles are selected from the group consisting ofsilver-plated glass spheres, sintered metal particles, silver-platedcopper particles, and conductive polymers.
 13. The method of claim 12wherein the sintered metal particles have bulk resistivities below about10⁻⁵ ohm-cm.
 14. The method of claim 1 wherein the extensible conductivecoating comprises conductive fibers and an extensible film.
 15. Aproduct manufactured according to the method of claim 1 .
 16. An EMIshield comprising: (a) a thermoformable film comprising a first side anda second side, wherein the thermoformable film is thermoformed into athree-dimensional shape; (b) an extensible conductive coating applied tothe thermoformable film; and (c) a compressible EMI gasket attached tothe thermoformable film.
 17. The EMI shield of claim 16 wherein theextensible conductive coating is applied to at least one of the firstside and the second side of the thermoformable film.
 18. The EMI shieldof claim 17 wherein the extensible conductive coating is appliedsubstantially uniformly to the at least one of the first side and thesecond side of the thermoformable film.
 19. The EMI shield of claim 17wherein the extensible conductive coating is applied selectively to atleast one zone and not another zone on the at least one of the firstside and the second side of the thermoformable film.
 20. The EMI shieldof claim 16 wherein the compressible EMI gasket comprises a mixture offoamable materials and conductive particles to form a foam mixture withan integral network of conductive particles.
 21. The EMI shield of claim20 wherein the foamable materials are a polyol component and anisocyonate component which form a urethane foam mixture.
 22. The EMIshield of claim 20 wherein the conductive particles are selected fromthe group consisting of silver-plated glass spheres, sintered metalparticles, silver-plated copper particles, and conductive polymers. 23.The EMI shield of claim 22 wherein the sintered metal particles havebulk resistivities below about 10⁻⁵ ohm-cm.
 24. The EMI shield of claim16 wherein the extensible conductive coating comprises conductive fibersand an extensible film.
 25. An extensible conductive coating comprisingconductive fibers and an extensible film.
 26. The extensible conductivecoating of claim 25 wherein the conductive fibers are selected from thegroup consisting of stainless steel fibers, silver metallized fibers,silver loaded, silver/copper flake, silver/nylon fiber, silver carbonfibers, tin over copper flash, and tin.
 27. The extensible conductivecoating of claim 25 wherein an outer surface of the conductive fibersare coated with a metal sufficient to produce bulk conductivity of thematerial per ASTM 991 to less than about 10 milliohm-cm.
 28. Theextensible conductive coating of claim 25 wherein the extensible film isselected from the group consisting of polypropylene, polyethylene,polystyrene, acrylonitrile-butydiene-styrene, styrene-acrylonitrile,polycarbonate, polyester, and polyamide.
 29. The EMI shield of claim 24, wherein the extensible film has a glass transition temperature lowerthan that of the thermoformable film.